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SHT20P Datasheet(PDF) 4 Page - List of Unclassifed Manufacturers

Part No. SHT20P
Description  DFN type package reflow solderable
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SHT20P Datasheet(HTML) 4 Page - List of Unclassifed Manufacturers

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Datasheet SHT20P
www.sensirion.com
Version 4 – May 2014
4/10
stencil apertures should be 0.1mm longer than PCB pads
and positioned with 0.1mm offset away from the centre of
the package. The die pad aperture should cover about 70
– 90% of the pad area – say up to 1.4mm x 2.3mm
centered on the thermal land area. It can also be split in
two openings.
Due to the low mounted height of the DFN, “no clean”
type 3 solder paste10 is recommended as well as Nitrogen
purge during reflow.
Figure 7 Soldering profile according to JEDEC standard. TP <=
260°C and tP < 30sec for Pb-free assembly. TL < 220°C and tL <
150sec. Ramp-up/down speeds shall be < 5°C/sec.
It is important to note that the diced edge or side faces of
the I/O pads may oxidise over time, therefore a solder fillet
may or may not form. Hence there is no guarantee for
solder joint fillet heights of any kind.
For soldering SHT2x, standard reflow soldering ovens may
be used. The sensor is qualified to withstand soldering
profile according to IPC/JEDEC J-STD-020 with peak
temperatures at 260°C during up to 30sec for Pb-free
assembly in IR/Convection reflow ovens (see Figure 7).
For manual soldering contact time must be limited to 5
seconds at up to 350°C.
Immediately after the exposure to high temperatures the
sensor may temporarily read a negative humidity offset
(typ. -1 to -2 %RH after reflow soldering). This offset
slowly disappears again by itself when the sensor is
exposed to ambient conditions (typ. within 1-3 days). If RH
testing is performed immediately after reflow soldering,
this offset should be considered when defining the test
limits.
In no case, neither after manual nor reflow soldering, a
board wash shall be applied. Therefore, and as mentioned
above, it is strongly recommended to use “no-clean” solder
paste. In case of applications with exposure of the sensor
to corrosive gases or condensed water (i.e. environments
with high relative humidity) the soldering pads shall be
sealed (e.g. conformal coating) to prevent loose contacts
or short cuts.
10 Solder types are related to the solder particle size in the paste: Type 3 covers
the size range of 25 – 45 µm (powder type 42).
2.2
Storage Conditions and Handling Instructions
Moisture Sensitivity Level (MSL) is 1, according to
IPC/JEDEC J-STD-020. At the same time, it is
recommended to further process the sensors within 1 year
after date of delivery.
It is of great importance to understand that a humidity
sensor is not a normal electronic component and needs to
be handled with care. Chemical vapors at high
concentration in combination with long exposure times
may offset the sensor reading.
For this reason it is recommended to store the sensors in
original packaging including the sealed ESD bag at
following conditions: Temperature shall be in the range of
10°C – 50°C and humidity at 20 – 60%RH (sensors that
are not stored in ESD bags). For sensors that have been
removed from the original packaging we recommend to
store them in ESD bags made of metal-in PE-HD11.
In manufacturing and transport the sensors shall be
prevented of high concentration of chemical solvents and
long exposure times. Out-gassing of glues, adhesive tapes
and stickers or out-gassing packaging material such as
bubble foils, foams, etc. shall be avoided. Manufacturing
area shall be well ventilated.
For more detailed information please consult the
document “Handling Instructions” or contact Sensirion.
2.3
Temperature Effects
Relative humidity reading strongly depends on
temperature. Therefore, it is essential to keep humidity
sensors at the same temperature as the air of which the
relative humidity is to be measured. In case of testing or
qualification the reference sensor and test sensor must
show equal temperature to allow for comparing humidity
readings.
If the sensor shares a PCB with electronic components
that produce heat it should be mounted in a way that
prevents heat transfer or keeps it as low as possible.
Measures to reduce heat transfer can be ventilation,
reduction of copper layers between the sensor and the
rest of the PCB or milling a slit into the PCB around the
sensor – see Figure 8.
11 For example, 3M antistatic bag, product “1910” with zipper.
Time
tP
TP
TL
TS (max)
tL
preheating
critical zone


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